PDL suppression on long-period fiber gratings by azimuthally isotropic exposure

We investigate a method to suppress the polarization-dependent loss (PDL) of long-period fiber gratings (LPFGs). We study the origins of the PDL and propose all azimuthally isotropic UV exposure to suppress the UV-induced birefringence and to realize low-PDL LPFGs. By using this technique and a low birefringent fiber together. the PDL of LPFGs can be reduced to a sufficiently low level required in high performance communication systems, Moreover the validity of our theoretical modeling is confirmed by the experimental results.